Well, for some of the newer users who seem to just put +Rep on their posts, this is how you add rep to a person.
How to Add Reputation:
If you find a post you like, find the person's "Add to
Users Reputation" and click on it.
The "Add to
Users Reputation" button looks like this.

You can find this Reputation button on the upper right part of a post like this.
Types of Reputation:

-Positive Reputation. Everybody loves this, this is "good" rep.

-Neutral Reputation. This means that the person was too new to the site, or doesn't have a high enough post count to add anything to your reputation.

-Negative Reputation. This is bad rep, please don't abuse this one.
Reputation points:
Reputation goes by points, if you get rep with a member with a lot of good rep, your rep will increase by more. To see your "Reputation Points" go to the USER CP. That's this:
You can then find your reputation points in the upper right hand corner of your Rep. Look here:
It also shows all of your reputation received.
I hope this guide helps the new people of GC, I took some time to make it and I hope you Enjoy it.
-AFD